1. Field of the Invention
The present invention relates to the field of materials and particularly to the field of graphene nanoribbons.
2. Related Art
Presented below is background information on certain aspects of the present invention as they may relate to technical features referred to in the detailed description, but not necessarily described in detail. The discussion below should not be construed as an admission as to the relevance of the information to the claimed invention or the prior art effect of the material described.
Graphene nanoribbons (GNRs) are materials with properties distinct from those of other carbon allotropes, as described in detail by Li et al 2008 Science 319: 1229; Wang et al 2008 Phys. Rev. Lett. 100: 206803; Chen et al 2007 Physica E 40: 228; Han et al 2007 Phys. Rev. Lett. 98: 206805; and Cresti et al 2008 Nano Res. 1: 361. The high carrier mobility of graphene has been described in detail by Novoselov et al 2004 Science 306: 666; Zhang et al 2005 Nature 438: 201; Novoselov et al 2005 Nature 438: 197; Berger et al 2006 Science 312: 1191; and Geim & Novoselov 2007 Natur. Mater. 6: 183. This offers the possibility of building high-performance graphene-based electronics. The all-semiconducting nature of sub-10-nm GNRs could bypass the problem of extreme chirality dependence of the metal or semiconductor nature of carbon nanotubes (CNTs) in future electronics. Recently, both theoretical and experimental work has shown that quantum confinement and edge effects introduce a band gap in narrow graphene ribbons independent of chirality, and the resulting GNR semiconductors can be used to make field-effect transistors (Nakada et al 1996 Phys. Rev. B 54:17954; Barone et al 2006 Nano Lett. 6: 2748; Son et al 2006 Phys. Rev. Lett. 97: 216803; Yang et al 2007 Phys. Rev. Lett. 99:186801; Li et al 2008 Science 319: 1229; Wang et al 2008 Phys. Rev. Lett. 100: 206803; Chen et al 2007 Physica E 40: 228; and Han et al 2007 Phys. Rev. Lett. 98: 206805).
Currently, making pristine GNRs using lithographic, chemical or sonochemical methods is challenging. Lithographic (Chen et al 2007, Physica. E 40: 228; Han et al 2007, Phys. Rev. Lett. 98: 206805; Tapaszto et al 2008 Nat. Nanotechnol. 3: 397), chemical (Datta et al 2008, Nano Lett. 8: 1912; Ci et al 2008, Nano Res. 1: 116; Campos et al 2009, Nano Lett. 9: 2600; Campos-Delgado et al 2008, Nano Lett. 8: 2773) and sonochemical (Li et al 2008, Science 319: 1229) methods have been developed to make GNRs. Lithographic patterning has been used to produce wide ribbons (>20 nm) from graphene sheets (Chen et al 2007 Physica E 40: 228; and Han et al 2007 Phys. Rev. Lett. 98: 206805), but the width and smoothness of the GNRs were limited by the resolution of the lithography and etching techniques. Bulk amounts of wide (20-300 nm) and few-layered (2-40) GNRs were synthesized by a chemical vapor deposition method (Campos-Delgado et al 2008 Nano Lett. 8:2773). Recently, GNR formation by unzipping carbon nanotubes (CNTs) has been reported (as described below). Two groups successfully unzipped multi-walled carbon nanotubes (MWNTs) in solution-phase by using potassium permanganate oxidation (Kosynkin et al 2009 Nature 458: 872) and lithium and ammonia reactions (Cano-Marquez et al 2009, Nano Lett. 9: 1527), respectively. Only wide, heavily oxidized and defective GNRs were made due to extensive oxidation involved in the unzipping process. More recently, unzipping methods such as catalytic cutting (Elias et al 2009, Nano Lett. ASAP DOI: 10.1021/n1901631z) and high current pulse burning (Kim et al 2009, Appl. Phys. Lett. 95: 083103) have been reported, but the quality and yield of GNRs were unknown. Thus far, it has been difficult to obtain GNRs with smooth edges and controllable widths at high yields.
CNTs are considered to be GNRs rolled up into seamless tubes and the synthesis, size control, placement and alignment control of nanotubes have been widely investigated, and established (Dai 2002 Surf. Sci. 500:218; and Jorio et al 2008 in Carbon Nanotubes: Advanced Topics in the Synthesis, Structure, Properties and Applications—Springer). The invention described below relates to a discovery that, CNTs can be unzipped to form GNRs with structural control. One great challenge in converting CNTs to GNRs is to develop ways of cleaving CNTs in the longitudinal direction without rapid etching along the circumference.